Machines such as, for example, excavators, loaders, dozers, and motor graders, often use multiple tool actuators supplied with hydraulic fluid from a hydraulic pump to accomplish a variety of tasks. These tool actuators are typically pilot controlled such that, as an operator moves an input device (e.g., a joystick) an amount of pilot fluid is directed to a tool control valve to move the tool control valve. As the tool control valve is moved, a proportional amount of fluid is directed from the pump to the tool actuators. Various hydraulic control strategies have been implemented to control the amount of fluid flow between the pump and the tool actuators, including a load sensing control strategy.
Load sensing control strategies measure a pressure differential between a maximum load pressure of a plurality of tool actuators and a pump delivery pressure. A controller typically receives the pressure differential data and controls a displacement of the pump to deliver the maximum load demand. More specifically, load sensing control systems attempt to control pump displacement to maintain a desired buffer pressure between pump delivery pressure and the maximum load pressure. In order to maintain pump control stability, the pump is typically controlled to deliver fluid at an excess pressure to ensure the maximum load pressure is available to the tool actuators.
A control system for regulating pump output is described in U.S. Pat. No. 6,374,722 (the '722 patent) issued to Du et al. on Apr. 23, 2002. The '722 patent describes a system with a variable displacement pump, a controller, a sensor, a servo valve, a servomechanism, and a servo control operable to command adjustment of a swashplate tilt angle and, hence, regulate pump discharge pressure. In the '722 patent, the controller commands adjustment of the swashplate tilt angle based upon the pump discharge pressure. The sensor generates a signal indicative of pump discharge pressure and sends this signal to the controller. Upon receiving the signal and determining an error, the controller commands the servomechanism of the servo valve to vary the swashplate tilt angle, which adjusts pump output.
Although the system of the '722 patent may increase regulation precision of pump discharge pressure, certain disadvantages may still persist. For example, a lag between the time at which an error occurs and the time when the error is corrected may cause delayed system response. Further, due to the lag, the system may be difficult to tune and prone to instability.
The disclosed system is directed to overcoming one or more of the problems set forth above and/or other problems with prior systems.